Burning lime and like co-yielding materials



April 7,1953 .m. RUIZ I 2,634,119

BURNING LIME AND LIKE CO YIELDING MATERIALS Filed Nov. 13, 1947 PRESSURE GAS w GAS CLEANER R COMPRESSOR INVEN TOR. JOSEPH J. RUIZ QZ/LLY ZWM ATTORNEYS Patented Apr. 7, 1953 BURNING" D LIKE C02 -'-Y'IELDIN'G' MATERIAI2S Joseph .LlRuiz,v Cleveland, Ohimassignor-to Basic. :Refractoriea, Inc.,- Cleveland, Ohio, a corpora! tionaof Ohio AppiicationNovember 13, 1947', SeriaPNo. 785,820

,1- Glaim. 1 1- In burning lime, a well knownprocedure involvescharglng the stone; in size of two-inch pieces or larger; together with coke, intothe top of- :a vertical; kilngWhilga'inior combustion is suppl'iedtby a-bloweratthe bottom. 'This procedure Y hasathe disadvantage "of tending to yield; products tacking desirable uniformity and. freedom from. unconverted cores. Anothervery serious disadvantagewhere theoff carbon dioxide is utilized is the requirementoipickup-compressors tottaketthe gas'leav-ing vthellriln and: compress it to: va, suiiieient pressure head for feeding to apparatus-sue s carbonators, etc, for-its use. Inrsuchv practice, l the characteristic is operation of rtthe calcining izone at atmospheric pressure. 'lneaccordance with the present invention, the :calciningtandthe "discharge-of carbon dioxide catriedison under"super -atmospheric "pressure, andawithradvantages: in operation and products as :will :appear from? the following description.

, To the: accomplishment of' the foregoing and related endsi'thednventi'on, then, comprises the meatures hereinafterifully described and particu- Jarly'pointeda outL-in the claim, the following description and-the annexed drawingsetting forth imdetaiL certainaiillustrative embodiments of" the invention, .these1beingr indicative, however, of but :acifewcof the various: waysin which the principle of." thezinventiommay be a employed;

. 1il1es:sole.-':figure: is a schematic verticalsecview" of .an illustrative equipment: in which thegpnocess'mayhe carriertout.

1ncalciningiin accordance with-the present insvention thmapparatus employe'd may vary. (Dne iformaexoi iapparatus; shown in the drawing, in-

, valves .awrerticalshaft kiln. K .to which crushed ends; isoias-itc provide succession valved gas lock zon'esl the-bottom: of the kilnsKyand then disichargedi Super-atmospheric pressure 'ismai-nrtainedz 'ini the; :kiln, compressed clean and cool z-being forc'ed by: compressor A into---the bottone; and. there; being no: release, the combustion -:gas,=proceeds=under :pressure through its pipe- G ":to: a ,cleanenand: underrpressurez toxaistoragepoint icmpoininofmsagei IbiiS: or course-r required to: be

'2, capable.v of withstanding the operating-1, pressures involved, and in genera1':may. include:xa' metal jacket with refractory lining, and :in :upright placement, and having compressing means for forcing air intothe bottomat .avrate 1301116 termine the. operating pressure.-whichiisutozbe maintained: in the calcining chamberorki'ln, and since the lime or calcined product. must; be discharged from the; highpressureQ ,containerxto the outside atmosphere, an intermediate cliargev chamber with, acut-off valve. :leadingssto the. calcining chamber. ands-another cut-olivalve at :the discharge 1 point to the :ratmosphere, in:- chides the. generally suitable equipment: 1301:1361:- mit the calcined material vto the passedsouti-of the :calciningchambeainto the discharge compartment, and .by appropriatelalternate opera,- tion of: the valves to: discharge; the product .to the outsider At the toplofithe'ki'ln oricalcining chamber, again a separate compartmentuwitlrva valve; between the calcining; chamber and. aavalve at, the inlet of such: compartment, ypermitsiyfeed of, rawmaterial, and; with; appropriate alternate "operation of ,such valves, movement: of. the ma.- .terial withouti'interfering with the high pressure maintenancerLin: the calcining chamber. In ten- -gineering practice, the general; construction of such gas-locks known, and be "adapted variously. One: form of apparatus which. may be employed: in: carrying-rout theaprocess set fployedgmost commonly. asolid;carbonaceonsiiuel, :preierably coke, ris to bezemployed 'andziiniamixsturera-longxwith; theucrushed stone Depending upon-general; conditions; thezproportione such coke or the like-:may; bervaried, butansnally itnis preferred. to employ about 1am equal number-act stone, and fuelzparticles; With the valv between the, calcining: chamber an the ncharging 'vcomr apartment closed: and the-valve at the inlet otithe charging, compartment open, the pressureezcne ,:in the calcining: chamber is duly maintained, but the stone charge cam be. introduced 'il117011i1i1l6 charging compartmentr Then, on closing 'the in let valve; and opening: the valveito the calcining chamher;,,the; material-maybe emptied: thereinto.

fuel is progressively heated up to the point of combustion in the central zone of the calcining chamber, while the gas passing from the top under high pressure has given up substantially all of its heat and is fed into scrubbers or other cleaning means and then to point of use. e. g. carbonators, or storage. Exit gas temperatures not much above atmospheric are thus readily attained. Simultaneously, since compressed air at high pressure is being forced into the bottom of the calcining chamber, in proceeding counterconcurrently through the calcined product coming from the center combustion zone, a heat exchange zone on the calcined product is thus effective to progressively heat up the air to the combustion zone and progressively cool the calcined lime or magnesia or like product such that it may be passed to the discharge compartment, the outlet valve of the latter being closed and its inlet valve next to the calcining chamber being opened, and then on closing the inlet valve and opening the outlet valve the calcined product having given up its heat to the incoming air is discharged to the atmosphere at a temperature relatively low and permitting easy handling.

As the operating pressure maintained on the kiln is determined by the pressure of the compressed air forced in at the bottom, it is seen that the control is relatively simple, and since no compressors are required operating on the discharge gases from the kiln, notable advantages result. Cool clean air is handled by the compressing plant, and the volume is considerably less than would have to be handled by compressors to operate on the exit gas made up of the produced carbon dioxide both of the cal- .cination and the fuel combustion plus the residual nitrogen from air supplies for combustion. In an illustrative equipment thus, the power required to operate the air compressors in the present process is only about 72% of what would be required to operate the kiln at customary atmospheric pressure and compression pick-up of the exit gas. Additionally, the present procedure eliminates the difficulties and high costs of main- .tenance of compressors operating on exit gas. .Such gas, even after going through cleanermeans, carries condensate substances and sulpliur dioxide from the fuel, which are destructive on compressor equipment.

In the customary operation at atmospheric pressure, the stone fed for calcining must be relatively large, two inches and more, because the draft through a mass of stone is progressively cut down as the stone size is decreased, and such size is the minimum practicable in atmospheric pressure operation. However, in super-atmospheric pressure as in the present invention, since creases and th linear velocity decreases and the overeall eifect of increasing the operating pres- .sure is to reduce the pressure loss proportionately; and since the pressure loss is also inversely proportional to the size of the stone, it is seen that for a given drop through the stone charge, the size of stone can be reduced proportionately to the increase in total pressure. Thus, in operating, for example, at 60 lbs. p. s. i. abs., the stone can be one-quarter the size of that for a process operating at atmospheric pressure, and yet the power required to force the air and gases through the kiln is approximately one-quarter that required when operating with the top at atmospheric pressure, since it would be required to compress only one-quarter the air volume to provide for the pressure loss through the kiln. For th same reason, if it be assumed that the same amount of power is to be used to drive the gases through a kiln operating at 60 lbs. p. s. i. abs. as is used for atmospheric pressure operation, the size of the stone can be one-sixteenth smaller; or it would vary inversely to the square of the operating pressure.

The stone for the present process may thus be sized in accordance with the operating pressure which is to be maintained, and in general may be less than one-half inch. Conveniently, an operating pressure of at least 50 lbs. p. s. i. abs., preferably around 60 lbs., may be employed. The advantages of the invention, however, may be realized in proportion, with lower or higher pressures, all super-atmospheric.

An important result of this use of smaller size stone in the charge is the improvement of the uniformity of calcining, the amounts of unburned cores and over-burned stone being proportionally reduced. And, it becomes possible to calcine stone which is too small to be handled by customary atmospheric-pressure calcining. As the stone size is reduced, the size of the solid fuel or coke also can be reduced, and operation becomes possible for instance with even coke breeze. which is of very low cost compared with lump coke. Economies in fuel cost result.

The capacity, or the tonnage of stone that can be calcined in a given kiln volume, depends on the stone surface area and on the mass or weight of air and gases flowing through it. Operating under a pressure of several atmospheres and with stone size thus materially reduced, the stone area per given volume is increased, thereby increasing the capacity of the kiln, since the heat transfer rate from the gases to the stone is increased. The heat transfer rate and kiln capacity increase also as the weight or mass flow for a given cross-sectional area is increased, and as the gas pressure is increased the density or mass per volume increases. For a given linear gas velocity and pressure loss through the kiln,

by operating under pressures above atmospheric,

an increase in kiln capacity results. The rate of combustion of fuel also increases with the pressure, being a function of the partial pressure of oxygen.

It is interesting that the calcination of calcium and magnesium carbonates follows the .thermo-dynamic properties of boiling water, that at a pressure of 3206.2 p. s. i. abs. at a temperature of 7-05.4 F., the liquid and the saturated vapor contain the same total heat (no heat of vaporization). Thus, as the calcining reaction is carried on at pressures substantially above atmospheric, the heat required for the reaction decreases, with a corresponding decrease in fuel requirement. Since also a pressurized kiln is considerably smaller for the same capacity, it follows that the heat loss from the shell is less than that for a kiln for atmospheric pressure operation, and a reduction in fuel requirements results.

As a result of decrease in amount of fuel required per ton of stone calcined, the per cent of CO2 in the exit gas increases, since less air is required per ton of stone decomposed and consequently the amount of diluent nitrogen is proportionately reduced. With the present process, richer CO2 gas is obtained, and this becomes of importance for many kinds of usages.

From the standpoint of lime or magnesia products, it is seen that a calcining process operating under super-atmospheric pressure as here contemplated, provides a uniformity which has long been desired, and from the standpoint of carbon dioxide produced, it provides a product of high content and directly available in carbonating operations or other usages. At the same time, in the total operation the only compressor action required to maintain the kiln pressure and discharge the exit gas at desired pressure is at the inlet of the equipment and operating on cool, clean air. correspondingly there is a very substantial saving in compressor maintenance and upkeep as compared with any system having compressors operating on off-gas which causes deposits in the cylinders and valves and which also contains more or less sulphur dioxide from the fuel combustion.

Other modes of applying the principle of th invention may be employed, change being made as regards the detail described, provided the features stated in the following claim, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

In a process of calcining, passing a mixture of fuel and material to be calcined having a particle size of about one-half inch or less through sucoession-valved gas-lock zones, then passing the whole mixture as a unitary substantially vertical, continuously downwardly sinking column of particles substantially maintaining their positions relative to each other through a first heat exchange zone in which hot product gases wholly passing countercurrently to the column preheat the mixture, then through a second lower contiguous combustion zone in which the calcined product is formed, and then through a third still lower contiguous heat exchange zone in which the heat of the calcined product preheats countercurrently incoming air, and simultaneously with passage of the continuously downwardly moving column, feeding low velocity compressed clean and cool air into said third zone substantially directly countercurrently to the downwardly moving column so as to cool the calcined product and to maintain super-atmospheric pressure within the three zones and proper combustion in the second zone, without upsetting the non-turbulent downward flow of particles, drawing on the calcined cooled product through succession-valved air-lock zones below the column, and passing the cooled product gases from the first heat exchange zone under its maintained super-atmospheric pressure.

JOSEPH J. RUIZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 152 Garber et a1. Mar. 25, 1837 1,836,526 Clement Dec. 15, 1931 2,037,809 MacMullin Apr. 21, 1936 2,080,981 Haas May 18, 1937 2,168,312 Baily Aug. 8, 1939 2,469,989 Pyzel May 10, 1949 2,528,098 White Oct. 31, 1950 2,529,366 Bauer Nov. '7, 1950 OTHER REFERENCES Thorp, "Dictionary of Applied Chemistry, Longmans, Green 8: Co., New York, 1938, 4th ed.. vol. II, pages 206-208. 

